Urea adducts of organic sulfur



Un d Stews, Pa en 7 UREA ADDUCTS OF ORGANIC SULFUR COMPOUNDS Robert A. Dinerstein, Park Forest, 111., assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana No Drawing. Application June 7, 1952, Serial No. 292,391

6 Claims. (Cl. 260-965) This invention relates to noveladducts of urea and organic sulfur compounds and to the separation of organic sulfur compounds from mixtures of organic liquids. More particularly, the invention relates to urea adducts of straight-chain compounds of carbon combined with sulfur. In an advantageous embodiment, the invention relates to the separation of straight-chain organic sulfur compounds from organic sulfur compounds of branched or cyclic structure. I

One object of the invention is to convert organic sulfur compounds into regenerable derivatives of lower volatility. Another object is to prepare solid adducts of organic sulfur compounds. A further object is to separate straight-chain sulfur compounds from admixture with petroleum, coal distillates, or other liquid media. A still further object is to effect the separation of straight-chain organic sulfur compounds from water-insoluble liquids in which they are dissolved and from which they can ordinarily be removed only by destruction of the sulfur com pounds by chemical reagents, by heat, or the like; it is therefore a specific object to extract the straight-chain sulfur compounds by interaction with a reagent from which they can be completely regenerated without chemical change. Other objects will be apparent from the present description.

In therefining of gasoline, kerosene, and certain lubricating oils, it has heretofore been desirable to remove sulfur compounds naturally occurring therein. The sulfur is usually found in these stocks in the form of mercaptans, sulfides, disulfides, or cyclic compounds such as thiophenes. Because of their chemical activity andsolvent properties, it has been posisble to remove the cyclic sulfur compounds with some success, for example, by treatment with sulfuric acid. The lower molecular weight mercaptans up to about C also can be extracted, for example with alkaline reagents. Sulfides and disulfides, however, and particularly the former, have been quite difiicult to separate, and the difficulty is especially great with the straight-chain or normal compounds.

I have now found that the normal organic sulfides, disulfides, and mercaptans having six carbon atoms or more in the molecule undergo a reaction with urea under certain conditions, forming crystalline derivatives from which t e remainder of the liquid in which the sulfur compounds are found can be separated. These derivatives have been variously termed complexes, adducts, associations, and clathrate compounds in the art. On treatment of the separated. urea-sulfur compound adduct with a urea solvent, such as water, alcohol, or the like, or by applying heat, the adduct is. readily decomposed and the constituents thereof are regenerated. The reaction is particularly well adapted to removal of mercaptans, sulfides, and disulfides .from heavy naphthas and kerosenes obtained from crude oils of the Pennsylvania or Mid-Continent type, in which a substantial proportion of the sulfur compounds are of the normal type as opposed to branchedchain or cyclic types. The reaction is not adapted to the ov of u r remnants from stra sh -chai i y r r 2,804,451 Patented Aug. 27, 1957 carbons of more than six carbon atoms which themselves ing selective action of the urea on the sulfur compounds.

In carrying out a process based on my new reaction, a sulfur-containing hydrocarbon of the defined class is agitated at about room temperature, preferably in the range of about 10 to 65 C., with powdered urea. It is preferred to activate the urea with a small amount of water or an organic solvent for urea such as alcohol or acetone to hasten the reaction. Methanol, ethanol or propanol are especially suitable. If water is chosen for this purpose, I prefer to use about one-quarter mole of water per mole of urea, and proportions in excess of one mole per mole are undesirable. The presence of as much as three moles of water per mole of urea substantially prevents the reaction. When methanol is used, the best results are obtained with about one-quarter. to one-half mole per mole of urea, although larger proportions of methanol, for example one to four moles, may be used when convenient. Still larger proportions of ethanol can be used.

After agitating the mixture for about five minutes to two hours, preferably about forty-five minutes, the reaction, which is exothermic, is substantially complete. The crystalline product of urea and sulfur compound is then separated, for example, by filtration, decantation, or centrifuging. Complete removal of the mother liquid from the crystalline mass may be obtained by washing with a suitable solvent with which the urea does not react, such as benzene, pentane, isooctane, or carbon tetrachloride. If it is desired to regenerate the sulfur compound, the crystalline product is then decomposed by adding an excess of water, methanol, or ethanol, or by heating it to the decomposition temperature, for example about to C., whereupon the sulfur compound separates either as a liquid layer or as a vapor, depending upon its boiling point. The urea solution in water, methanol, etc., is distilled to remove the solvent. and can then be used again for further sulfur compound extraction. If the decomposition is effected by heating, the urea can be cooled and used directly or the melted urea can be dispersed directly in the liquid to be treated.

After the sulfur compounds have been recovered from the urea reaction products, they may be purified by fractional distillation where there is a substantial difference in their boiling points. Where there is little difference in boiling point, the mercaptans can be separated from the sulfides and disulfides by extraction with alkaline reagents. The disulfides can be separated from the sulfides by treatment with certain reducing agents, the sulfides being unaffected thereby, while the disulfides are converted to mercaptans of lower boiling point which are readily separated from the sulfides by distillation.

The amount of urea required for the reaction is usually about one mole for each methylene (CH2) group in the extractable material present. Thus, on extracting a sulfur compound such a n-butyl sulfide containing six methylene groups, six moles of urea are required per mole of the sulfur compound. If other urea-reactive straightchain compounds of six or more carbon atoms are present in the charging stock, additional urea can be employed suflicient to react with them. An excess of urea may be employed when convenient, although this is undesirable from the standpoint of operating efficiency. If less than the amount of urea required for complete reaction is employed, based on the foregoing, then a selective reaction can be obtained, leaving unreacted in the reaction mixture certain of the straight-chain materials which would otherwise be removed.

My invention is applicable broadly to the treatment of straight-chain organic sulfur compounds containing six or more carbon atoms in the molecule, including mercaptans, sulfides, disulfides, higher sulfides, and the like. The foregoing classes of compounds are variously named in the literature, and are intended to include n-alkanethiols, thioethers, di-n-alkyl sulfides, di-n-alkyl thioethers, di-n-alkyl disulfides, and the like; n-butyl sulfide, for example, is commonly referred to as n-butyl thioether, di-n-butyl sulfides," or di-n-butyl thioether, and sometimes as n-butylthia-n-butane or l-(n-butylthia)-n-butane. Among the suitable compounds are nbutyl disulfide, n-butyl sulfide, n-octyl sulfide, n-dodecyl mercaptan, n-hexyl mercaptan, n-octyl mercaptan, n-octyl methyl thioether, n-butyl n-propyl thioether, n-propyl disulfide, n-octyl disulfide, n-heptyl mercaptan, n-hexyl sulfide, n-tetradecyl sulfide, and the like. Unsaturated homologues of the foregoing compounds and classes of compounds are also suitable.

My invention will be more fully understood from the following specific examples:

Example 1 n-Dodecyl mercaptan (25 milliliters) was agitated at room temperature with 50 milliliters of urea-saturated methanol. The resulting precipitate was filtered ofi, washed with ethyl ether, and dried, yielding a white crystalline solid melting around 132 C. The solid, when commingled with an excess of water, was decomposed thereby into an aqueous urea phase and a n-dodecyl mercaptan oil phase.

Example 2 n-Dodecyl mercaptan (7.90 grams) was commingled in a calorimeter with urea (60 grams) and methanol (128 grams), and it was observed that the ensuing reaction produced a temperature rise of 3.61 C. From the foregoing data it was calculated that the heat of formation of the urea adduct of n-dodecyl mercaptan was 13.9 kilocalories per mole of the mercaptan.

In a similar test, the reaction of urea with n-octyl disulfide was found to release 14.9 kilocalories per mole of the sulfur compound. The ratio of urea to n-octyl disulfide in the resulting adduct was about 12, corresponding to slightly less than one mole of urea per methylene group.

In another similar test, the reaction of urea with nheptyl mercaptan released 5.87 kilocalories per mole of the mercaptan.

In another similar test, the reaction of urea with n hexyl sulfide released 12.01 kilocalories per mole of the sulfide.

Example 3 n-Octyl thioether (25 milliliters) was commingled at room temperature with 50 milliliters of a saturated solution of urea in methanol. The resulting slurry was filtered and the solid was washed with ethyl ether and dried. A white powder was obtained thereby, consisting of an adduct of n-octyl thioether and urea, and melting around 132 C. When stirred with water, the adduct decomposed and liberated the n-octyl thioether as an oil phase.

Example 4 n-Propyl disulfide (30 grams, 0.2 mole) was stirred for 2 hours at room temperature, approximately 70 F., with urea (120 grams, 2 moles) and methanol (80 milliliters, 2 moles). The resulting reaction slurry was filtered, and the filter cake was divided into two equal portions for further processing. From the filtrate, 8 grams of n-propyl disulfide were recovered.

One portion of the filter cake was washed with 100 milliliters of isooctane. The washings yielded 6 grams of n-propyl disulfide on evaporation of the isooctane. After being dried, the solids were a white, crystalline powder, melting at approximately 132 C. On being decomposed with water, the solids liberated 3 grams of n-propyl disulfide. r

The second portion of the filter cake was washed with milliliters of methanol saturated with urea to avoid decomposition. The washing yielded 5 grams of n-propyl disulfide after dilution with water and evaporation of the methanol. The solids, when dried and decomposed with water, yielded 5 grams of n-propyl disulfide.

From the foregoing tests, it was calculated that approximately four moles of urea reacted with each mole of the n-propyl disulfide.

Example 5 Example 6 The following tests were made to determine whether ethyl disulfide will react with urea. Ethyl disulfide (31 grams, 0.25 mole) was contacted with urea (150 grams, 2.5 moles) and methanol (100 milliliters, 2.5 moles) for a period of three hours at room temperature, about 70 F. The reaction mixture was then filtered, and from the filtrate were recovered 28 grams of the original ethyl disulfide or substantially the original amount, indicating that no reaction had taken place. When this experiment was repeated with. 400 milliliters 10 moles) of methanol in the reaction mixture, the same result was obtained.

In a series of similar experiments, the following organic sulfur compounds also failed to form adducts with urea:

Methyl disulfide Isopropyl disulfide Isobutyl disulfide Tertiary-octyl mercaptan One of the applications of my new reaction is in the separation of normal organic sulfur compounds from admixture with branched-chain sulfur compounds; for example, I may separate n-propyl sulfide from admixture with isopropyl sulfide practically quantitatively by ureaadduct formation with the n-propyl sulfide. Moreover, because of the nearly quantitative nature of my new reaction, it is convenient for use in the analysis of mixtures of sulfur-containing carbon compounds.

The urea adducts of straight-chain organic sulfur compounds are white, crystalline solids, stable at ordinary temperatures, and in general melting with decomposition around C. They are highly useful materials, combining as they do in one molecule an abundance of available nitrogen and sulfur. The urea adducts of the normally volatile sulfur compounds have the special advantage of supplying such compounds at low volatility and in readily released form. The organic sulfide adducts may conveniently be converted into aliphatic sulfonic acids by blowing with air in the presence of nitrogen oxides, nitric acid, or other oxidation catalyst. Other uses will be apparent to those skilled in the art.

While I have described my invention with reference to certain specific embodiments and applications thereof, it is to be understood that such embodiments and applications are purely illustrative and not to be construed as limitations. In general it can be said that any modifications or equivalents that would ordinarily occur to one skilled in the art are to be considered as lying within the scope of my invention.

This application is a continuation-in-part of my application Serial No. 794,198, filed December 27, 1947, now abandoned.

Having thus described my invention, I claim:

1. In a process for separating an organic sulfur compound selected from the class consisting of straight-chain aliphatic mercaptans, sulfides, and disulfides having at least six carbon atoms in the molecule from a mixture thereof with another organic sulfur compound selected from the class consisting of straight-chain aliphatic mercaptans, sulfides, and disulfides having fewer than six carbon atoms in the molecule, branched-chain and cyclic mercaptans, sulfides, and disulfides, and heterocyclic sulfur compounds, the steps which comprise contacting said mixture with urea under urea-adduct-forming conditions, whereby a solid adduct is selectively formed by said urea and said straight-chain sulfur compound having at least six carbon atoms in the molecule, separating said adduct from the resulting reaction mixture, decomposing said adduct, and recovering said straight-chain sulfur compound having at least six carbon atoms in the molecule therefrom.

2. The process of claim 1 wherein said straight-chain aliphatic sulfur compound having at least six carbon atoms in the molecule is a mercaptan.

3. The process of claim 1 wherein said straight-chain aliphatic sulfur compound having at least six carbon atoms in the molecule is a sulfide.

4. The process of claim 1 wherein said straight-chain aliphatic sulfur compound having at least six carbon atoms in the molecule is a disulfide.

5. In a process for separating a straight-chain aliphatic sulfur compound of the class consisting of mercaptans, sulfides and disulfides having at least six carbon atoms in the molecule from a mixture thereof with a branchedchain aliphatic sulfur compound of the class consisting of mercaptans, sulfides, and disulfides, the steps which com- References Cited in the file of this patent UNITED STATES PATENTS 2,253,638 McKennon Aug. 26, 1941 2,445,655 Allen et a1. July 20, 1948 2,499,820 Fetterly Mar. 7, 1950 2,520,715 Fetterly Aug. 29, 1950 2,549,372 Fetterly Apr. 17, 1951 OTHER REFERENCES Conant: The Chemistry of Organic Compounds,"

(1939) Macmillan Co., N. Y., pages 264 to 267.

Technical Oil Mission, Reel 143, Translation of Bengens German patent application 0. Z. 12,438, 6 pages (1946). 

1. IN A PROCESS FOR SEPARATING AN ORGANIC SULFUR COMPOUND SELECTED FROM THE CLASS CONSISTING OF STRAIGHT-CHAIN ALIPHATIC MERCAPTANS, SULFIDES, AND DISULFIDES HAVING AT LEAST SIX CARBON ATOMS IN THE MOLECULE FROM A MIXTURE THEREOF WITH ANOTHER ORGANIC SULFUR COMPOUND SELECTED FROM THE CLASS CONSISTING OF STRAIGHT-CHAIN ALIPHATIC MERCAPTANS, SULFIDES, AND DISULFIDES HAVING FEWER THAN SIX CARBON ATOMS IN THE MOLECULE, BRANCHED-CHAIN AND CYCLIC MERCAPTANS, SULFIDES, AND DISULFIDES, AND HETEROCYCLIC SULFUR COMPOUNDS, THE STEPS WHICH COMPRISE CONTACTING SAID MIXTURE WITH UREA UNDER UREA-ADDUCT-FORMING CONDITIONS, WHEREBY A SOLID ADDUCT IS SELECTIVELY FORMED BY SAID UREA AND SAID STRAIGHT-CHAIN SULFUR COMPOUND HAVING AT LEAST SIX CARBON ATOMS IN THE MOLECULE, SEPARATING SAID ADDUCT FROM THE RESULTING REACTION MIXTURE, DECOMPOSING SAID ADDUCT, AND RECOVERING SAID STRAIGHT-CHAIN SULFUR COMPOUND THAT AT LEAST SIX CARBON ATOMS IN THE MOLECULE THEREFROM. 